Laser irradiation apparatus

ABSTRACT

In annealing of a non-single crystal silicon film by a linear laser beam, it is performed so as irradiation tracks caused by the linear laser beam do not remain in the silicon film. Laser light is partitioned by an integrally formed cylindrical array lens, and is composed into a single uniform laser beam on an irradiation surface by a cylindrical lens and a doublet cylindrical lens. The integrally formed cylindrical array lens is used, and therefore cylindrical lenses structuring this array lens can be made very fine. It thus becomes possible to partition the laser light into a large number of partitions, and the uniformity of the laser beam on the irradiation surface is increased. Very few laser irradiation tracks remain on the silicon film annealed by the very uniform laser beam.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for manufacturing asemiconductor device having a circuit constituted by a thin film. Forexample, the present invention relates to a device for manufacturing anelectrooptical device typified by a liquid display device and theconstitution of an electric device having. the electrooptical device asa part. In this connection, in the present specification, asemiconductor device designates in general a device capable offunctioning by the use of semiconductor characteristics and includes theabove electrooptical device and electric device.

2. Description of the Related Art

In recent years, research and development have been widely conducted onthe technologies for performing a laser annealing processing to anamorphous semiconductor film or a crystalline semiconductor film(semiconductor film which is not a single crystal but a polycrystal or amicro-crystal), that is, non-single crystal semiconductor film formed onan insulating substrate such as a glass substrate or the like tocrystallize the non-single crystal semiconductor film or to improve itscrystallinity. A silicon film is often used as the above semiconductorfilm.

A glass substrate has advantages that it is cheap and has goodworkability and is easy to make a large area substrate in comparisonwith a quartz substrate which has been conventionally used. This isbecause the above research and development have been carried out. Also,it is because the melting point of the glass substrate is low that alaser is widely used for crystallizing the semiconductor film. The lasercan apply high energy only to a non-single crystal film withoutincreasing the temperature of the substrate too much.

The crystalline silicon film is called a polycrystalline silicon film ora polycrystalline semiconductor film because it is made of many crystalgrains. Since the crystalline silicon film subjected to a laserannealing processing has high mobility, a thin film transistor(hereinafter referred to as TFT) is formed by the use of the crystallinesilicon film and, for example, is widely used for a monolithic liquidcrystal electrooptical device having a glass substrate on which TFTs fordriving a pixel and for a driving circuit are formed.

Also, a laser annealing method of transforming the high-power laser beamof a pulse oscillation such as an excimer laser into a square spotseveral cm square or a linear beam 10 cm or more in length at anirradiate surface by the use of an optical system and of scanning asemiconductor film with the laser beam (or moving a spot irradiated withthe laser beam relatively to an irradiate surface) has been widely usedbecause it increases mass productivity and is excellent in an industrialview point.

In particular, when a linear laser beam is used, the whole irradiatesurface is irradiated with the linear laser beam only by scanning theirradiate surface in the direction perpendicular to the direction of theline of the linear laser beam, which therefore produces high massproductivity. In contrast to this, when a spot-like laser beam is used,the irradiate surface needs to be scanned with the laser beam in theback-and-forth direction and in the right-and-left direction. Theirradiate surface is scanned with the linear laser beam in the directionperpendicular to the direction of the line of the linear laser beambecause the direction is the most efficient scanning direction. Themethod of using the linear laser beam into which the laser beam emittedfrom the excimer laser of pulse oscillation is transformed by the use ofa suitable optical system for the laser annealing processing has becomea mainstream technology.

In FIG. 1 is shown an example of the constitution of an optical systemfor transforming the cross section of the laser beam into a linear shapeat an irradiate surface. This constitution not only transforms the crosssection of the laser beam into the linear shape but also homogenizes theenergy of the laser beam at the irradiate surface. In general, anoptical system homogenizing the energy of the beam is called a beamhomogenizer.

The side view is explained first. A laser beam leaving from a laseroscillator 101 is partitioned in a direction perpendicular to themovement direction of the laser beam by cylindrical array lenses 102 aand 102 b. This direction is referred to as a vertical directionthroughout this specification. There are four partitions with thisstructure. The partitioned laser beams are once collected into a singlelaser beam by a cylindrical lens 104. This is then reflected by a mirror107, and once again condensed into one laser beam on an irradiationsurface 109 by a doublet cylindrical lens 108. The doublet cylindricallens refers to a lens composed of two cylindrical lenses. The linearlaser beam is thus given energy uniformity in the width direction, andthe length of the width direction is thus determined.

The top view is explained next. The laser beam leaving from the laseroscillator 101 is partitioned in a direction perpendicular to themovement direction of the laser beam, and perpendicular to the verticaldirection, by a cylindrical array lens 103. This direction is referredto as a horizontal direction throughout this specification. There areseven partitions with this structure. The laser beams are next made intoa single beam on the irradiation surface 109 by the cylindrical lens104. The linear laser beam is thus given energy uniformity in thelongitudinal direction, and the length is thus determined.

The above lenses are manufactured by synthetic quartz in order torespond to the excimer laser. Further, coating of the lens surface isperformed so as to make it very transmissive to the excimer laser. Thetransmissivity of the excimer laser by one lens thus becomes equal to orgreater than 99%.

By performing laser annealing on the entire surface of a non-singlecrystal silicon film by irradiating the linear laser beam, processed bythe above constitution, while gradually shifting it in the widthdirection, crystallization can be performed and crystallinity can beincreased.

A model method of manufacturing a semiconductor film which becomes anirradiation object is shown next. First, a 5 inch diagonal Corning 1737substrate having a thickness of 0.7 mm is prepared. A SiO₂ film (siliconoxide film) of 200 nm thickness is deposited on the substrate by using aplasma CVD apparatus, and an amorphous silicon film (hereafter referredto as an a-Si film) of 50 nm thickness is formed on the surface of theSiO₂ film.

The substrate is heated for 1 hour at a temperature of 500° C. in anitrogen atmosphere, decreasing the hydrogen concentration within thefilms. The laser resistance of the film is thus significantly increased.

A Lambda Corp. XeCl excimer laser (wavelength 308 nm, pulse width 30 nm)L3308 is used as a laser apparatus. The laser apparatus is a pulseemission type, and possesses the capability of delivering energy of 500mJ/pulse. The size. of the laser beam is 10×30 mm (both values arehalf-widths) at the exit of the beam. The shape of a laser beamgenerated by an excimer laser is generally a rectangular shape, andexpressed as an aspect ratio, is in the range of approximately 3 to 5.The strength of the laser beam shows a Gaussian distribution, in whichits strength increases as it approaches the center. The size of thelaser beam is transformed into a 125 mm×0.4 mm linear laser beam havinga uniform energy distribution by an optical system possessing thestructure shown in FIG. 1.

According to experiments performed by the applicant of the presentinvention, when the laser is irradiated on the above semiconductor film,the overlap pitch is most suitable at approximately {fraction (1/10)} ofthe width (half width) of the linear laser beam. The uniformity ofcrystallinity within the film is thus increased. In the above example,the half width is 0.4 mm, and therefore the pulse frequency of theexcimer laser is set to 30 hertz, the scanning speed is set to 1.0 mm/s,and the laser beam is irradiated. The energy density of the laser beamin the irradiation surface is 420 mJ/cm² at this time. The method usedhere to crystallize the semiconductor film using the linear laser beamis an extremely general method.

If the pulse emission excimer laser beam is processed into a linearshape by an optical system such as the one stated above, and then if thelinear laser beam is irradiated while scanning, on a non-single crystalsilicon film, for example, then a polycrystalline silicon film isobtained.

A phenomenon of film striping running in the vertical and horizontaldirections is conspicuous when observing the polycrystalline siliconfilm obtained. (See FIG. 2.)

The semiconductor characteristics differ with each of the stripes, andtherefore if the striped state film is used when manufacturing anintegrated driver and pixel (system on panel) liquid crystal display, aproblem develops in which the strips are output to the screen as are.The stripes output on the screen are caused by non-uniform crystallinityin both a driver portion and a pixel portion. This problem is beingimproved by improving the film quality of the laser beam and the qualityof the non-single crystal silicon film which becomes the irradiationobject of the laser beam, and has been improved to such an extent that,depending upon the liquid crystal display manufactured, it does notbecome a problem. However, when manufacturing a liquid crystal displaywith higher definition and good characteristics, the above stripingnonetheless becomes a problem. The present invention is for solving thisproblem.

The main reasons that the above striped pattern is generated are: energydiffusion near the edges in the width direction of the linear laser beam(expressing a state in which the energy is attenuated as the edge of thelaser beam is approached); and non-uniformity of energy in thelongitudinal direction of the linear laser beam. An energy diffusionregion is defined throughout this specification as a region having anenergy density equal to or less than 90% of the maximum energy densitywithin the linear laser beam.

The energy diffusion near the edge in the width direction of the linearlaser beam becomes a cause of the formation of the stripe pattern in adirection parallel to the longitudinal direction of the linear laserbeam. Furthermore, the energy non-uniformity in the longitudinaldirection of the linear laser beam becomes a cause of the formation ofthe stripe pattern in a direction orthogonal to the longitudinaldirection of the linear laser beam.

In order to resolve the problem of non-uniform energy in thelongitudinal direction of the linear laser beam, an increase in thenumber of cylindrical array lenses 102 and 103 is considered.

The number of partitions of the cylindrical array lenses in the aboveexample is four vertical partitions and seven horizontal partitions, fora total of 28 partitions. Tests for increasing the uniformity of thelaser anneal by increasing the number of partitions have been performedover many years. Some examples of such tests are given below.

The size of one cylindrical lens structuring the four partitioncylindrical array lens is a width of 3 mm and a length of 50 mm, longand narrow, in the above example. These values, if expressed as anaspect ratio relating to the width and the length of one cylindricallens, are 50/3, or approximately 16.7. On the other hand, the size ofone cylindrical lens structuring the seven partition cylindrical arraylens is a width of 7 mm and a length of 50 mm, relatively fat, in theabove example. When expressed as an aspect ratio, this is 50/7, orapproximately 7.1.

It is therefore easy to make the seven partition cylindrical array lensthinner from the viewpoint of a manufacturing technique. However, if theenergy distribution of the linear laser beam obtained by the above 28partitions is investigated in detail, it is understood that the energynear the centerline in the width direction of the linear laser beamclearly differs from the energy near the edges of the linear laser beamin the same direction. The energy, which possesses a higher energy,differs from every time optical adjustment is performed. Therefore, nomatter how much the number of partitions of the seven partitioncylindrical array lenses is increased, the energy distribution withinthe linear laser beam will not tend toward a uniform direction, and itwill only have a non-uniform distribution in the width direction of thelinear laser beam.

Based on the above considerations, the only way to manufacture anoptical system through which a very uniform laser anneal effect can beexpected is to increase the number of partitions of the four partitioncylindrical array lens.

However, the lenses structuring the optical system are of syntheticquartz, which is difficult to process. Further, the cylindrical lens of3 mm width and 50 mm length structuring the cylindrical array lens givenin the above example has a shape which is extremely slender as a lens,and therefore a high degree of technical skill is required forindependent manufacturing of the lenses.

The above cylindrical array lens is made into a cylindrical array lensby mutually joining the cylindrical lenses manufactured one by one. Or,the cylindrical array is made by exposure to high temperature afterforming the array, causing unification. Therefore, each cylindrical lensis initially separate.

In order to give each of the cylindrical lenses sufficient strength andprecision, it is necessary for the aspect ratio between the lens widthand the lens length to be at least equal to or less than 20. This valueis based on experience of the applicant of the present invention. Forexample, in addition to the above cylindrical array lens, by forming 8cylindrical lenses having a length of 60 mm and a thickness of 2 mm,lining up the cylindrical lenses in the width direction and putting theminto a frame, the formation of the cylindrical array lens can beperformed, but the precision is completely insufficient. In addition,the directionality of the laser beams passing through each cylindricallens becomes so scattered that it can be understood by the naked eye,and the energy uniformity of the linear laser beam obtained becomesworse than that of the example shown previously. This example has anaspect ratio of 30.

For example, the width of all of the cylindrical lenses contained in thecylindrical array lens 102 in the example of the optical system shown inFIG. 1 is halved, and the number of partitions is doubled to 8partitions, then the aspect ratio of one cylindrical lens contained inthe cylindrical array lens 102 becomes 33, becoming larger than that ofthe cylindrical array lens of 2 mm width formed earlier.

In order to increase the number of partitions without increasing theaspect ratio of the cylindrical lenses structuring the cylindrical arraylens, a method of expanding the laser beam output from the laseroscillator by using a beam expander can be used, but if the aberrationof the doublet cylindrical lens 108 is not reduced by the amount thatthe laser beam is expanded, then a new problem develops in which thelaser beam does not sufficiently unify on the irradiation surface.

An example of specification of the doublet cylindrical lens 108 is shownbelow, in accordance with FIG. 7. The doublet cylindrical lens 108 has afocal distance of 175 mm, a width of 70 mm, and a length of 160 mm, witha center thickness of 31 mm. The above lens has curvature in the widthdirection. The radius of curvature of a laser beam incidence surface 701is 125 mm, the radius of curvature of a next surface 702 is 69 mm, andthe center distance between the surfaces 701 and 702 is set to 10 mm.One cylindrical lens can be made with this structure. A secondcylindrical lens has a laser beam incidence surface 703 placed at acenter distance of 1 mm away from the surface 702. The radius ofcurvature of the laser beam incidence surface 703 is 75 mm, and theradius of curvature of a next surface 704 is set to −226 mm. The centerdistance between the surfaces 703 and 704 is 20 mm. Symbols attached tothe radius of curvature show the curvature direction.

An example of computing the spot size in the focal point of a doubletlens possessing a curvature similar to that of the doublet cylindricallens 108 by using the optical design software Zemax is shown in FIGS.12A and 12B. FIG. 12A shows the beam spot when parallel light with awavelength of 308 nm and a diameter of 24 mm is incident on the abovedoublet lens. The spot size becomes approximately 50 μm. Therefore, whenthe laser beam is incident on the doublet cylindrical lens 108, if thewidth of the laser beam is assumed to be 24 mm, then it can be foundthat the diffusion in the width direction of the linear laser beambecomes on the order of 50 μm. The width of the linear laser beam madeby the optical system in the above example is 400 μm, and therefore, theratio of the above width to the width of the linear laser beam in thediffusion region exceeds a ratio of 10%. This diffusion becomes a causeof the formation of horizontal stripes in a silicon film.

On the other hand, FIG. 12B shows the beam spot when parallel light witha wavelength of 308 nm and a diameter of 12 mm is incident on the abovedoublet lens. The spot size becomes equal to or less than 4 μm. Thiscorresponds to diffusion on the order of 1% of the linear laser beamwidth. Demanding a higher precision than this is difficult from thestandpoint of precision of lens manufacture.

From the above simulation results, it can be understood that in order tosuppress the influence of the aberration of the doublet cylindrical lens108, the size of the incident laser beam should be made as small aspossible. Or, generally, the doublet cylindrical lens 108 must bereplaced by an aspherical lens, or it must be replaced by a highprecision lens equal to or better than a triplet lens structured bythree lenses.

With present techniques, it is extremely difficult to ashpericallyprocess synthetic quartz. Further, forming a triplet lens is also notadvisable from the viewpoint of cost or adjustment. The thinner thewidth of the laser beam generated by the oscillator is made, the morethe aberration of the doublet cylindrical lens 108 can be suppressed,and therefore it is not preferable to make the size of the laser beamgenerated by the oscillator much greater than on the order of 10×30 mm(with 10 mm corresponding to the width of the laser beam).

Considering the above, it can be expected that, with the presentstructure, the number of partitions of the four partition cylindricalarray lens can only be increased to around five partition. With thisnumber of partitions, the energy uniformity of the linear laser beamwill not change from the present state. Although it is understood thatthe surface area of a portion for the edge energy diffusion in the widthdirection of the linear laser beam increases, the current situation isthat the number of laser beam partitions is increased by a method ofexpanding the width of the laser beam using a beam expander to securethe above uniformity.

SUMMARY OF THE INVENTION

An object of the present invention is to eliminate the above problems byproviding a laser irradiation apparatus for obtaining a polycrystallinesilicon film having a little stripe patterns.

The applicant of the present invention solves this problem by using acylindrical array lens mentioned below as a substitute for thecylindrical array lens 102.

In other words, the cylindrical array lens used by the present inventionis integrally formed in order to ensure strength and precision. Thistype of cylindrical lens can be formed by etching or shaving, forexample. The meaning of integrally formed is that mutually adjacentcylindrical lenses become integrated before forming the lens surface.

The aspect ratio of one cylindrical lens structuring the cylindricalarray lens may be made equal to or greater than 20 without problems instrength or precision because the above cylindrical array lens isintegrally formed.

The following can be given as an example of a current integrally formedcylindrical array lens: for example, there is one in which from 10 to 50cylindrical lenses having a 1 mm width are lined up, with a length of 50mm and a radius of curvature of 20 mm. The directionality of a laserbeam passing through each of the cylindrical lenses has a precision of+/−1%. Further, the focal distance of the respective lenses is heldwithin a range of +/−3%. (Catalog values)

The applicant of the present invention was lead to an idea of firstincorporating the above integrally formed cylindrical array lens intothe optical system for forming the linear laser beam. It is necessary touse the integrally formed cylindrical array lens in the optical systemfor forming the linear laser beam because the linear laser beam isextremely thin (having an aspect ratio equal to or greater than 100).

The aspect ratio of the cylindrical lenses of 1 mm width structuring theabove integrally formed cylindrical array lens is 50. The effectresulting from integrally forming the cylindrical array lens is thatsuch a minute lens can be manufactured.

The present invention has been invented based on the progress of suchtechniques. Namely, the present invention is a laser irradiationapparatus for irradiating a laser beam having a cross-sectional shapewhich is linear in an irradiation surface, comprising:

a laser oscillator for generating the laser beam;

an optical system; and

a stage which moves in at least one direction,

wherein the optical system has:

a first optical system (corresponding to 401 a and 401 b in FIG. 4)comprising an integrally formed cylindrical array lens which fulfills arole of partitioning the laser beam in a direction which isperpendicular to the direction in which the laser beam is moving;

a second optical system (corresponding to 402 and 406) that fulfills arole of joining the partitioned laser beams by the first optical systemon the irradiation surface;

a third optical system (corresponding to 403 in FIG. 4) which fulfills arole of partitioning the laser beam in a direction which is in a planeperpendicular to the perpendicular direction and perpendicular to thedirection in which the laser beam is moving; and

a fourth optical system (corresponding to 404 in FIG. 4) that fulfills arole of joining the partitioned laser beams by the third optical systemon the irradiation surface,

wherein the aspect ratio relating to the width and the length of onecylindrical lens forming the integrally formed cylindrical array lens isequal to or greater than 20.

In addition, another structure is a laser irradiation apparatus forirradiating a laser beam having a cross-sectional shape which is linearin an irradiation surface, comprising:

a laser oscillator for generating a rectangular-shape laser beam;

an optical system; and

a stage which moves in at least one direction,

wherein the optical system has:

a first optical system (corresponding to 401 a and 401 b in FIG. 4)comprising

an integrally formed cylindrical array lens which fulfills a role ofpartitioning the laser beam in a direction which is perpendicular to thedirection in which the laser beam is moving;

a second optical system (corresponding to 402 and 406) that fulfills arole of joining the partitioned laser beams by the first optical systemon the irradiation surface;

a third optical system (corresponding to 403 in FIG. 4) which fulfills arole of partitioning the laser beam in a direction which is in a planeperpendicular to the perpendicular direction and perpendicular to thedirection in which the laser beam is moving; and

a fourth optical system (corresponding to 404 in FIG. 4) that fulfills arole of joining the partitioned laser beams by the third optical systemon the irradiation surface,

wherein the width of one cylindrical lens forming the integrally formedcylindrical array lens is equal to or less than ⅙ of the length of theshort side of the rectangular-shape laser beam.

The rectangular-shape laser beam is defined by a region in which theenergy is equal to or greater than 5% of the maximum energy of theenergy distribution within the face of the rectangular-shape laser beam,and the length of the short side of the rectangular shape laser beam isdefined by the length of the short side of the largest rectangular shapein the above region.

Making the present invention equal to or less than ⅙ is because it ispossible to have up to five partitions with present techniques, and thestructure of the present invention is necessary to have six or morepartitions.

As to the above any structure of the present invention, if the abovelongitudinal direction of the laser beam, which has a linearcross-sectional shape on the irradiation surface, and the movementdirection of the above stage which moves in at least one direction forma right angle, then the productivity is high, which is preferable.

As to the above any structure of the present invention, if the abovelaser oscillator is one which generates an excimer laser, then a largeoutput can be obtained and the productivity can be increased, which ispreferable. In addition to the excimer laser, YAG laser harmonics existas a pulse emission laser apparatus with which a large output can beobtained at a wavelength region with a high absorption coefficient withrespect to the semiconductor film. This may also be used with thepresent invention.

As to the above any structure of the present invention, if the number ofcylindrical lenses structuring the integrally formed cylindrical arraylens is equal to or greater than six, then a very uniform laser annealbecomes possible.

If each of the above laser irradiation apparatus has a load-unloadchamber, a transfer chamber, a preheating chamber, a laser irradiationchamber, and an annealing chamber, then it-can be used for large-scaleproduction, which is preferable.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is an optical system for forming a linear laser beam;

FIG. 2 is a diagram showing the state of a silicon film on which alinear laser beam has been irradiated while scanning;

FIG. 3 is a diagram showing an example of an optical system for forminga linear laser beam disclosed by the present invention;

FIG. 4 is a diagram showing an example of a laser irradiation apparatusdisclosed by the present invention;

FIGS. 5A and 5B are diagrams for explaining points which must beconsidered when designing an optical system for forming a linear laserbeam;

FIG. 6 is a diagram showing an optical system for forming a linear laserbeam in an embodiment of the present invention;

FIG. 7 is a diagram showing a portion of an optical system for forming alinear laser beam in an embodiment of the present invention;

FIG. 8 is a diagram showing an optical system for forming a linear laserbeam in an embodiment of the present invention;

FIG. 9 is a diagram showing a laser irradiation apparatus;

FIG. 10 is a diagram showing a simulation performed by optical designsoftware;

FIG. 11 is a diagram showing a simulation performed by optical designsoftware; and

FIGS. 12A and 12B are diagrams showing simulations performed by opticaldesign software.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, an example is shown of irradiating a laser beam processed into alinear shape onto an irradiation surface of a substrate having a 5 inchdiagonal as an irradiation object.

FIG. 3 shows a laser irradiation apparatus. An example of an apparatusirradiating a linear laser beam on a substrate is shown in FIG. 3. Thecomposition of the apparatus is explained below.

A laser beam generated from a laser oscillator 301 and having a size of10×30 mm is made incident to an optical system 303 via a mirror 302 a, amirror 302 b, and a mirror 302 c. The mirrors are installed in order tocontrol the incidence direction of the laser beam with respect to theoptical system. First, the laser beam is turned toward the top by themirror 302 a, the laser beam is next turned to the horizontal directionby the mirror 302 b, and is additionally turned in other horizontaldirections by the mirror 302 c.

The laser beam which leaves the optical system 303 goes to a mirror 304and is condensed as a linear laser beam 306 on the surface of asubstrate 307 by a doublet cylindrical lens 305. Reference numeral 308denotes a stage upon which the substrate 307 is placed. The stage 308scans in a right-angle direction with respect to the linear laser beam306 (in the direction of the arrows in the figures) by a motionmechanism 309. The laser beam is thus irradiated over the entire surfaceof the substrate 307. A mechanism such as a ball screw or a linear motoris used in the motion mechanism 309.

By suppressing the expansion angle of the laser beam by inserting a beamcollimator between any two of the above mirrors, the energy uniformityof the linear laser beam obtained is increased. It is good to controlthe expansion angle of the laser beam in the short side direction of thelaser beam. The angle of expansion in the short side direction of thelaser beam is generally on the order of 0.5 mrad.

Next, the composition of an optical system that determines theuniformity in the width direction of the linear laser beam, and itswidth, is explained in accordance with FIG. 4. Lenses 401 to 404 of FIG.4 are inside the optical system 303 of FIG. 3. The mirror 304 of FIG. 3is the same as a mirror 405 of FIG. 4. Further, the doublet cylindricallens 305 of FIG. 3 is the same as a doublet cylindrical lens 406 of FIG.4.

The laser beam is partitioned 12 times in the width direction by anintegrally formed cylindrical array lens 401 a made from 12 cylindricallenses. The laser beams are then made incident to the respectivecylindrical lenses of an integrally formed cylindrical array lens 401 bmade from 12 cylindrical lenses. The laser beams are condensed on asurface by a cylindrical lens 402. The laser beams are again separated,and are condensed on an irradiation surface 407 by a doublet cylindricallens 406. A mirror 405 is inserted within the light path, turning thelight path at a right angle.

The composition of an optical system for determining the uniformity inthe length direction of the linear laser beam, and its length, isexplained next. The cylindrical array lens 403 partitions the laser beaminto 7 partitions in the longitudinal direction. The laser beams arethen composed into one laser beam on the irradiation surface 407 whilebeing stretched by the cylindrical lens 404.

Thus a substrate on which a non-single crystal semiconductor film isformed is placed on the irradiation surface 407. By moving the substratein a direction having a right angle to the linear laser beam, the laserbeam can be irradiated over the entire surface of the substrate.

Note that in order to protect the optical system, an atmosphere such asnitrogen, which does not easily react with lens coating substances, maybe placed around the optical system. The optical system may also besealed in a protecting chamber in order to accomplish this. If coatedquartz is used in a laser window for entering and leaving the protectingchamber, then a high transmissivity equal to or greater than 99% can beobtained. Further, in order to prevent contamination of the substrate, achamber may be formed and laser beam irradiation may be performed in astate having the substrate inside the chamber.

The stage 308 is moved at a constant speed in a direction perpendicularto the longitudinal direction of the linear laser beam 306 by the motionmechanism 309.

If the substrate is irradiated with strong light and heated by aninfrared lamp in a location at which the laser beam is irradiated, whilethe laser beam is being irradiated, then a polycrystalline silicon filmhaving very high uniformity can be obtained.

The structure of the above optical system may be designed in accordancewith geometric optics. Specific examples of parameters such as the focallength of each lens are recorded in the embodiments of the presentinvention. Points that should be taken into consideration when designingthe structure are stated below.

First, the integrally formed cylindrical array lenses 401 a and 401 bshould be composed of convex lenses. This is because, if they arestructured by concave lenses, then the array lenses become difficult tomanufacture because of sharp portions which appear on the array lenses.

Further, when using convex lenses to structure the integrally formedcylindrical array lenses 401 a and 401 b, the minimum distance d betweenthe principal point (a technical term relating to lenses, and in generalthe distance between the principal point and the focal point is definedas the focal length) of the integrally formed cylindrical array lens 401a and the lens 401 b is made longer than 1.1f, and shorter than 1.9f.The symbol f denotes the focal length of the cylindrical array lens 401a here. The positional relationship between the integrally formedcylindrical array lenses 401 a and 401 b is shown in FIG. 5A.

The symbols used in FIG. 5A are explained. A plane 501 denotes a planecontaining all of the principal points of the cylindrical array lens 401a in the motion direction of the laser beam. A plane 503 denotes a planecontaining all of the focal points of the cylindrical array lens 401 ain the motion direction of the laser beam. A plane 505 denotes a planeseparated at a distance of 1.1f from the plane 501. A plane 507 denotesa plane separated at a distance of 1.9f from the plane 501. Thecylindrical array lens 401 b is placed within a region sandwiched by theplane 505 and the plane 507.

The minimum value 1.1f exists in order to prevent the energy density ofthe laser beam incident on the integrally formed cylindrical array lens401 b from becoming extremely high. The maximum value of 1.9f exists inorder to prevent one partitioned laser beam from being incident upon twoor more cylindrical lenses. It is preferable to reduce this range tobetween 1.3f and 1.7f. The design margin of the optical system can thusbe widened.

Another point that must be considered is that in order to suppressspherical aberration of the cylindrical lens 404, the minimum distance Dbetween the principal point of the cylindrical array lens 403 and thecylindrical lens 404 is set 1.3fl<D<3fl. The symbol fl denotes the focallength of the cylindrical array lens 403 here. FIG. 5B shows thepositional relationship between the cylindrical array lens 403 and thecylindrical lens 404.

The symbols used in FIG. 5B are explained. A plane 502 denotes a planecontaining all of the principal points of the cylindrical array lens 403in the motion direction of the laser beam. A plane 504 denotes a planecontaining all of the focal points of the cylindrical array lens 403 inthe motion direction of the laser beam. A plane 506 denotes a planeseparated at a distance of 1.3fl from the plane 502. A plane 508 denotesa plane separated at a distance of 3fl from the plane 502. Thecylindrical lens 404 is placed within a region sandwiched by the plane506 and the plane 508.

The minimum value 1.3fl exists in order that the energy density of thelaser beam striking the cylindrical lens 404 does not become large.Further, the maximum value of 3fl exists in order to suppress thespherical aberration of the cylindrical lens 404. The energydistribution of the linear laser beam thus becomes very uniform. Whenthe influence of the spherical aberration of the cylindrical lens 404 isstrong, a shape of the linear laser beam is not a rectangular shape, andtherefore, a width of the center part of the linear laser beam becomesnarrow.

An example such that the width of the center part of the linear laserbeam is narrow, as described above, is shown below. For instance, theminimum distance D is made equal to the sum of the focal length f1 ofthe cylindrical array lens 403 and the focal length f2 of thecylindrical lens 404.

This optical system combination plays a role of stretching out the laserbeam, and therefore f1<<f2.

The condition of 3fl<D(=f1+f2) is therefore satisfied in this case. Byincorporating an optical system which satisfies the condition 3fl<D, thelinear laser beam having an energy distribution such as that of FIG. 10,the result of modeling using the optical design software SOLSTIS, can beobtained. The dark portion in the figure is a portion of high energy. Inorder to make the energy distribution easy to see in the figure, theaspect ratio is expressed as one smaller than the actual aspect ratio.The linear laser beam expands slightly in edge portion in thelongitudinal direction of the linear laser beam, and becomes diffuse.This is due to the influence of the spherical aberration of thecylindrical lens 404.

In order to suppress the spherical aberration of the cylindrical lens404, a method of composing the lens of a plurality of lenses, or amethod of using a lens having a very small spherical aberration as theaspherical lens may be used. With present techniques, the manufacture ofaspherical lenses is extremely difficult, and if structuring the lens bya plurality of lenses is practical.

On the other hand, simulation results are shown in FIG. 11 for a case ofD within the range of 1.3fl<D <3fl, for example D=2fl. The results shownwere calculated using the same software as that of FIG. 10, and it canbe understood that the linear laser beam possesses an edge havingextremely high linearity.

The laser irradiation apparatus of the present invention can be appliednot only to a non-single crystal silicon film, but also to othernon-single crystal semiconductor films. For example, it can be appliedto non-single crystal semiconductor films such as germanium and diamond.

A semiconductor device, for example, a low temperature polysilicon TFTliquid crystal display device, may be manufactured by a known methodusing the semiconductor film crystallized by the above laser irradiationapparatus. In addition, other semiconductor devices designed by theoperator may also be manufactured.

Embodiment 1

An example of laser anneal of an a-Si film is shown in Embodiment 1.Further, concrete specifications of an optical system are shown. A 300Hz, 150 W XeCl excimer laser is used as a laser oscillator.

A Corning 1737 substrate with a thickness of 0.7 mm is used as asubstrate. The substrate has sufficient durability up to a temperatureof 600° C. A 200 nm SiO₂ film is deposited on one surface of thesubstrate by plasma CVD. In addition, an a-Si film having a thickness of55 nm is formed on the SiO? film. Other method of film deposition, suchas sputtering, may also be used.

The substrate with deposited films is heat treated for 1 hour at 500° C.in a nitrogen atmosphere, reducing the hydrogen concentration in thea-Si film. The laser resistance of the a-Si film can thus be greatlyincreased. A hydrogen concentration within the film on the order of 10²⁰atoms/cm³ is suitable.

The laser beam is processed into a linear laser beam having a length of160 mm and a width of 0.4 mm by the optical system shown in FIG. 4. Theoptical system shown in FIG. 4 is one example. The laser beam is imagedinto the linear shape on the a-Si film. The above size is the size ofthe laser beam when it is imaged.

The specific size, focal length, and positional relationship for each ofthe lenses of the optical system recorded in FIG. 4 are shown below.Quartz is used as the parent material for all of the optical systems.Further, a coating with which a transmissivity equal to or greater than99% can be obtained with respect to the 308 nm wavelength of the XeClexcimer laser beam is used as the coating.

The side view of FIG. 4 is explained first.

The integrally formed cylindrical array lenses 401 a and 401 b both havethe same shape, and are composed of 12 cylindrical lenses having a focallength of 41 mm, a width of 1 mm, a length of 50 mm, and a centerthickness of 2 mm. These lenses partition the laser beam in the verticaldirection. The reason that the lenses are formed having the identicalshape is mainly in order that the lens manufacturing cost can bereduced. It costs less to manufacture two of the same lens than to maketwo lenses which are different. If it is unreasonable from a designstandpoint to make the shapes identical, they may be structured withlenses that are mutually different.

The cylindrical lens 402 has a focal length of 375 mm, a width of 50 mm,a length of 50 mm, and a center thickness of 5 mm. This lens composesthe above laser beams, partitioned in the vertical direction, in acertain plane. The above plane is along the light path, and thereforethe light is again separated.

The doublet cylindrical lens 406 has a focal length of 175 mm, a widthof 70 mm, a length of 160 mm, and a center thickness of 31 mm. The abovelaser beams partitioned in the vertical direction are composed into oneon the irradiation surface by this lens.

The top view is explained next.

The cylindrical array lens 403 is composed of seven cylindrical lenseshaving a focal length of 43 mm, a width of 7 mm, a length of 50 mm, anda center thickness of 5 mm. The laser beam is-partitioned in thehorizontal direction by this lens.

The cylindrical lens 404 has a focal length of 1000 mm, a width of 50mm, a length of 50 mm, and a center thickness of 5 mm. The above laserbeams partitioned in the horizontal direction are composed into onelaser beam on the irradiation surface by this lens.

The above lenses all possess curvature in the width direction.

The arrangement of lenses may be in accordance with FIG. 6. Lensespossessing symbols identical to those of FIG. 4 are lenses havingidentical roles.

Namely, the distance between the integrally formed cylindrical arraylens 401 a and the integrally formed cylindrical array lens 401 b is 75mm, and the faces possessing curvature face mutually to the outside.

The distance between the integrally formed cylindrical array lens 401 band the cylindrical lens 402 is set to 50 mm.

The distance between the cylindrical lens 402 and the cylindrical arraylens 403 is 180 mm, and the distance between the cylindrical array lens403 and the cylindrical lens 404 is set to 87 mm. The respective facesof the cylindrical lens 402, the cylindrical array lens 403, and thecylindrical lens 404 possessing curvature face toward the laseroscillator.

The optical distance between the cylindrical lens 404 and the doubletcylindrical lens 406 is set to 720 mm. This is made to go via the mirror405 along the path. The laser light path is bent down by 90° by themirror 405.

The distance between the doublet cylindrical lens 406 and theirradiation surface 407 is 252 mm.

The shape of the doublet cylindrical lens 406 was explained above inaccordance with FIG. 7. Namely, it is the same as the doubletcylindrical lens 108.

When one wants to change the size of the linear laser beam, the focallength or the size of each portion of the optical system may beregulated in accordance with geometric optics.

If the energy distribution of the above linear laser beam in the lineardirection is within ±5%, then homogenous crystallization of the a-Sifilm can be performed. Preferably, if the energy distribution is within±3%, more preferably within ±1%, then very homogeneous crystallizationcan be performed. In order to make the energy distribution uniform, itis necessary to use precise lens alignment.

The maximum energy of the XeCl excimer laser used is 500 mJ/pulse. Thesurface area of the linear laser beam is 0.64 cm , and therefore themaximum energy density of the linear laser beam obtained is equal to orgreater than 500 mJ/cm².

The a-Si film is crystallized using the laser irradiation apparatus. Thelength of the linear laser beam is 160 mm, and therefore the laser beamcan be irradiated on nearly the entire surface of the substrate byscanning the linear laser beam in one direction with respect to a 5 inchsubstrate.

The irradiation conditions of Embodiment 1 are shown below.

Linear laser beam energy density: 420 mJ/cm²

Laser repetition frequency: 30 Hz

Substrate motion velocity: 1 mm/sec

Laser beam irradiation atmosphere: within clean room atmosphere equal toor less than class 1000

The above conditions are dependent upon such factors as the laseroscillator pulse width, the state of the film which is irradiated by thelaser beam, and the characteristics required by the device manufactured,and therefore the conditions may be suitably determined by the operatorin consideration of these factors.

The atmosphere during laser beam irradiation is not limited to theabove, and W the laser irradiation chamber may be surrounded by achamber, and H₂ May be substituted. Substitution of the atmosphere ismainly performed in order to prevent contamination of the substrate. Gassupply is performed through a gas cylinder. H₂, He, N₂, or Ar may alsobe used for the atmosphere. Further, a combination of these gases mayalso be used. Even if a vacuum is pulled on this atmosphere (equal to orless than 10⁻¹ torr), the contamination prevention effect remains.

The XeCl excimer laser is used as the laser oscillator, but other highoutput lasers may also be utilized. Other glass substrates such asCorning 7059 can be used in addition to Corning 1737 as the substrate. Aquartz substrate may also be used.

A semiconductor device, for example, a low temperature polysilicon TFTliquid crystal display device, may be formed by a known method using thesemiconductor film crystallized by the above laser irradiationapparatus. In addition, a semiconductor device proposed by the operatormay also be manufactured.

Embodiment 2

An example of irradiating a laser beam onto a poly-crystalline siliconfilm is shown in this Embodiment.

A Corning glass 1737 having a thickness of 0.7 mm is used as asubstrate. The substrate has sufficient durability if it is used under600° C. A SiO₂ film is formed in 200 nm on one surface of the substrateby plasma CVD. Further, an a-Si film is formed in 55 nm on the SiO₂film. Any other film forming method, for example, sputtering may beused.

Next, the above-mentioned a-Si film is crystallized by the methoddisclosed in Japanese Patent Application Laid-Open No. Hei 7-130652. Themethod will be described briefly in the following. The above a-Si filmis coated with a nickel acetate water solution having a concentration of10 ppm and then is heated in a nitrogen atmosphere at 550° C. for 4hours, whereby the a-Si film is crystallized. It is recommended that aspin coat method, for example, be used for applying the nickel acetatewater solution. The a-Si film to which nickel is added is crystallizedin a short period at low temperatures. It is thought that this isbecause the nickel acts as the seed crystal of crystal growth tofacilitate the crystal growth.

If the polycrystalline silicon film crystallized by the above method isirradiated with the laser beam, it has higher characteristics as amaterial of a semiconductor device. Accordingly, to improve thecharacteristics of the above * polycrystalline silicon film, the abovepolycrystalline silicon film is irradiated with the laser beam by usingthe laser irradiation device used in the preferred embodiment of thepresent invention. It is possible to utilize Embodiments 1 and 2 bycombination.

Embodiment 3

An example is shown in Embodiment 3 of using an optical system thatdiffers from the optical system shown by Embodiment 1. The opticalsystem is explained using FIG. 8. In Embodiment 3, an example in whichthe distance between the principal point of the integrally formedcylindrical array lens 401 a and 401 b is kept within the range of 1.3fto 1.7f is shown. The design margin of the optical system can thus bewidened. Note that f is the focal length of the integrally formedcylindrical array lens 401 a.

The laser beam is processed into a linear laser beam having a length of160 mm and a width of 0.4 mm on an irradiation surface by the opticalsystem shown in FIG. 8. A semiconductor film, which is an irradiationobject, is placed on the irradiation surface. The above size is the sizeof the linear laser beam on the irradiation surface. The semiconductorfilm is, for example, one made by the methods of manufacture recorded inEmbodiment 1 or Embodiment 2.

The specific size, focal length, and positional relationship for each ofthe lenses of the optical system recorded in FIG. 8 are shown below.Quartz is used as the parent material for all of the optical systems.Further, a coating with which a transmissivity equal to or greater than99% can be obtained with respect to the 308 μm wavelength of the XeClexcimer laser beam is used as the coating.

An integrally formed cylindrical array lens 801 a is composed of 12cylindrical lenses having a focal length of 61 mm, a width of 1 mm, alength of 50 mm, and a center thickness of 2 mm. The laser beam ispartitioned in the vertical direction by this lens.

An integrally formed cylindrical array lens 801 b is composed of 12cylindrical lenses having a focal length of 41 mm, a width of 1 mm, alength of 50 mm, and a center thickness of 2 mm.

A cylindrical lens 802 has a focal length of 375 mm, a width of 50 mm, alength of 50 mm, and a center thickness of 5 mm. This lens composes theabove laser beams, partitioned in the vertical direction, in a certainplane. The above plane is along the light path, and therefore the lightis again separated.

A doublet cylindrical lens 806 has a focal length of 175 mm, a width of70 mm, a length of 160 mm, and a center thickness of 31 mm. The abovelaser beams partitioned in the vertical direction are composed into oneon the irradiation surface by this lens.

A cylindrical array lens 803 is composed of seven cylindrical lenseshaving a focal length of 43 mm, a width of 7 mm, a length of 50 mm, anda center thickness of 5 mm. The laser beam is partitioned in thehorizontal direction by this lens.

A cylindrical lens 804 has a focal length of 1000 mm, a width of 50 mm,a length of 50 mm, and a center thickness of 5 mm. The above laser beamspartitioned in the horizontal direction are composed into one laser beamon the irradiation surface by this lens.

The above lenses all possess curvature in the width direction.

The arrangement of lenses may be in accordance with FIG. 8.

Namely, the distance between the integrally formed cylindrical arraylens 801 a and the integrally formed cylindrical array lens 801 b is 93mm, and the faces possessing curvature face mutually to the outside.

The distance between the integrally formed cylindrical array lens 801 band the cylindrical lens 802 is set to 70 mm.

The distance between the cylindrical lens 802 and the cylindrical arraylens 803 is 180 mm, and the distance between the cylindrical array lens803 and the cylindrical lens 804 is set to 87 mm. The respective facesof the cylindrical lens 802, the cylindrical array lens 803, and thecylindrical lens 804 possessing curvature face toward the laseroscillator.

The optical distance between the cylindrical lens 804 and the doubletcylindrical lens 806 is set to 720 mm. This is made to go via the mirror805 along the path. The laser light path is bent down by 90° by themirror 805.

The distance between the doublet cylindrical lens 806 and theirradiation surface 807 is 252 mm.

The shape of the doublet cylindrical lens 806 used is the same as thatof the doublet cylindrical lens 406.

When one wants to change the size of the linear laser beam, the focallength or the size of each portion of the optical system may beregulated in accordance with geometric optics.

If the energy distribution of the above linear laser beam in the lineardirection is within ±5%, then homogenous crystallization of the a-Sifilm can be performed. Preferably, if the energy distribution is within±3%, more preferably within ±1% then very homogeneous crystallizationcan be performed. In order to make the energy distribution uniform, itis necessary to use precise lens alignment.

A semiconductor device, for example, a low temperature polysilicon TFTliquid crystal display device, may be formed by a known method using thesemiconductor film crystallized by the above laser irradiationapparatus. In addition, a semiconductor device proposed by the operatormay also be manufactured.

Embodiment 4

An example of a laser irradiation apparatus for mass production is shownin A. Embodiment 4 in accordance with FIG. 9. FIG. 9 is a top view ofthe laser irradiation apparatus.

A substrate is carried from a load-unload chamber 901 by a conveyorrobot arm 903 set in a transfer chamber 902. The substrate is firstcarried to a preheating chamber 905, after position alignment in analignment chamber 904. The substrate is heated in advance to apredetermined substrate temperature, for example, on the order of 300°C., by using a heater such as an infrared lamp heater. The substrate issubsequently set in a laser irradiation chamber 907 via a gate valve906. The gate valve 906 is then closed.

The laser beam, after being output from a laser oscillator 900 shown byEmbodiment 1, is processed into a linear laser beam on a radiationsurface within the laser irradiation chamber 907 by passing through anoptical system 909, being bent 90° downward by a mirror set directlyabove a quartz window 910 but not shown in the figure, and through thequartz window 910. The laser beam is irradiated on the substrate set onthe irradiation surface. The optical system stated above may be used forthe optical system 909. Further, an optical system based on that opticalsystem may be used.

Before irradiation of the laser beam, the laser irradiation chamber 907is pulled to a high vacuum (10⁻³ Pa) using a vacuum pump 911. Or, adesired atmosphere may be made by using the vacuum pump 911 and a gascylinder 912. The atmosphere may be Ar, H₂, or a combination of thesegases as mentioned above.

By next scanning the substrate by using a motion mechanism 913 whileirradiating the laser beam, the substrate is irradiated by the linearlaser beam. An infrared lamp not shown in the figure may also be exposedat this time on a portion in which the linear laser beam is beingirradiated.

After completion of the laser beam irradiation, the substrate is carriedto a cooling chamber 908, and after annealing, the substrate is returnedto the load-unload chamber 901 via the alignment chamber 904. Byrepeating this series of movements, laser annealing can be performed ona plurality of substrates.

Embodiment 4 can be used in combination with the embodiment mode of thepresent invention or with other embodiments.

What is claimed is:
 1. A laser irradiation apparatus comprising: a laseroscillator for generating a laser beam; an optical system for processinga cross-sectional shape of the laser beam into a linear shape on anirradiation surface; and a stage which moves in at least one direction,wherein said optical system comprises: a first optical system comprisingan integrally formed cylindrical array lens for partitioning the laserbeam in a direction which is perpendicular to the direction in which thelaser beam is moving; a second optical system for joining thepartitioned laser beams by said first optical system on the irradiationsurface; a third optical system for partitioning the laser beam in adirection which is in a plane perpendicular to the perpendiculardirection and perpendicular to the direction in which the laser beam ismoving; and a fourth optical system for joining the partitioned laserbeams by said third optical system on the irradiation surface, whereinthe aspect ratio relating to the width and the length of one cylindricallens constituting said integrally formed cylindrical array lens is equalto or greater than
 20. 2. The laser irradiation apparatus according toclaim 1, wherein: the longitudinal direction of the laser beam which hasa linear cross-sectional shape on the irradiation surface; and themovement direction of the stage which moves in at least one direction,form a right angle.
 3. The laser irradiation apparatus according toclaim 1, wherein said laser oscillator is an oscillator which generatesan excimer laser.
 4. The laser irradiation apparatus according to claim1, wherein said laser irradiation apparatus has a load-unload chamber, atransfer chamber, a robot arm, and a laser irradiation chamber.
 5. Alaser irradiation apparatus comprising: a laser oscillator forgenerating a laser beam having a rectangular-shape cross section; anoptical system for processing a cross-sectional shape of the laser beaminto a linear shape on an irradiation surface; and a stage which movesin at least one direction, wherein said optical system comprises: afirst optical system comprising an integrally formed cylindrical arraylens for partitioning the laser beam in a direction which isperpendicular to the direction in which the laser beam is moving; asecond optical system for joining the partitioned laser beams by thefirst optical system on the irradiation surface; a third optical systemfor partitioning the laser beam in a direction which is in a planeperpendicular to the perpendicular direction and perpendicular to thedirection in which the laser beam is moving; and a fourth optical systemfor joining the partitioned laser beams by the third optical system onthe irradiation surface, wherein the width of one cylindrical lensconstituting said integrally formed cylindrical array lens is equal toor less than ⅙ of the length of the short side of the laser beam.
 6. Thelaser irradiation apparatus according to claim 5, wherein: the laserbeam is defined by a region in which the energy is equal to or greaterthan 5% of the maximum energy of the energy distribution within the faceof the laser beam; and the length of the short side of the laser beam isdefined by the length of the short side of the largest rectangular-shapecross section in said region.
 7. The laser irradiation apparatusaccording to claim 5, wherein: the longitudinal direction of the laserbeam which has a linear cross-sectional shape on the irradiationsurface; and the movement direction of the stage which moves in at leastone direction; form a right angle.
 8. The laser irradiation apparatusaccording to claim 5, wherein said laser oscillator is an oscillatorwhich generates an excimer laser.
 9. The laser irradiation apparatusaccording to claim 5, wherein said laser irradiation apparatus has aload-unload chamber, a transfer chamber, a robot arm, and a laserirradiation chamber.
 10. A laser irradiation apparatus comprising: alaser oscillator for generating a laser beam; an optical system forprocessing a cross-sectional shape of the laser beam into a linear shapeon an irradiation surface; and a stage which moves in at least onedirection, wherein said optical system comprises: a first optical systemcomprising two cylindrical, array lenses for partitioning the laser beamin a first direction which is perpendicular to a second direction inwhich the laser beam is moving; a second optical system for joining thepartitioned laser beams by said first optical system on the irradiationsurface; a third optical system for partitioning the laser beam in athird direction which is perpendicular to said first direction andperpendicular to said second direction; and a fourth optical system forjoining the partitioned laser beams by said third optical system on theirradiation surface.
 11. The laser irradiation apparatus according toclaim 10, wherein: the longitudinal direction of the laser beam whichhas a linear cross-sectional shape on the irradiation surface; and themovement direction of the stage which moves in at least one direction;form a right angle.
 12. The laser irradiation apparatus according toclaim 10, wherein said laser oscillator is an oscillator which generatesan excimer laser.
 13. The laser irradiation apparatus according to claim10, wherein said laser irradiation apparatus has a load-unload chamber,a transfer chamber, a robot arm, and a laser irradiation chamber.
 14. Alaser irradiation apparatus comprising: a laser oscillator forgenerating a laser beam; an optical system for processing across-sectional shape of the laser beam into a linear shape on anirradiation surface; and a stage which moves in at least one direction,wherein said optical system comprises: a first optical system comprisingan integrally formed cylindrical array lens for partitioning the laserbeam in a first direction which is perpendicular to a second directionin which the laser beam is moving; a second optical system for joiningthe partitioned laser beams by said first optical system on theirradiation surface; a third optical system for partitioning the laserbeam in a third direction which is perpendicular to said first directionand perpendicular to said second direction; and a fourth optical systemfor joining the partitioned laser beams by said third optical system onthe irradiation surface, wherein the aspect ratio relating to the widthand the length of one cylindrical lens constituting said integrallyformed cylindrical array lens is equal to or greater than
 20. 15. Thelaser irradiation apparatus according to claim 14, wherein: thelongitudinal direction of the laser beam which has a linearcross-sectional shape on the irradiation surface; and the movementdirection of the stage which moves in at least one direction; form aright angle.
 16. The laser irradiation apparatus according to claim 14,wherein said laser oscillator is an oscillator which generates anexcimer laser.
 17. The laser irradiation apparatus according to claim14, wherein said laser irradiation apparatus has a load-unload chamber,a transfer chamber, a robot arm, and a laser irradiation chamber.
 18. Alaser irradiation apparatus comprising: a laser oscillator forgenerating a laser beam having a rectangular-shape cross section; anoptical system for processing a cross-sectional shape of the laser beaminto a linear shape on an irradiation surface; and a stage which movesin at least one direction, wherein said optical system comprises: afirst optical system comprising an integrally formed cylindrical arraylens for partitioning the laser beam in a first direction which isperpendicular to a second direction in which the laser beam is moving; asecond optical system for joining the partitioned laser beams by saidfirst optical system on the irradiation surface; a third optical systemfor partitioning the laser beam in a third direction which isperpendicular to said first direction and perpendicular to said seconddirection; and a fourth optical system for joining the partitioned laserbeams by said third optical system on the irradiation surface, whereinthe width of one cylindrical lens constituting said integrally formedcylindrical array lens is equal to or less than ⅙ of the length of theshort side of the laser beam.
 19. The laser irradiation apparatusaccording to claim 5, wherein: the laser beam is defined by a region inwhich the energy is equal to or greater than 5% of the maximum energy ofthe energy distribution within the face of the laser beam; and thelength of the short side of the laser beam is defined by the length ofthe short side of the largest rectangular-shape cross section in saidregion.
 20. The laser irradiation apparatus according to claim 19,wherein: the longitudinal direction of the laser beam which has a linearcross-sectional shape on the irradiation surface; and the movementdirection of the stage which moves in at least one direction; form aright angle.
 21. The laser irradiation apparatus according to claim 19,wherein said laser oscillator is an oscillator which generates anexcimer laser.
 22. The laser irradiation apparatus according to claim19, wherein said laser irradiation apparatus has a load-unload chamber,a transfer chamber, a robot arm, and a laser irradiation chamber.
 23. Amethod for manufacturing a semiconductor device comprising the steps of:forming a semiconductor film over a substrate; crystallizing saidsemiconductor film by irradiating a linear laser beam, wherein saidlinear laser beam is generated by a laser irradiation apparatus, saidlaser irradiation apparatus comprising: a laser oscillator forgenerating a laser beam; an optical system for processing across-sectional shape of the laser beam into a linear shape on anirradiation surface; and a stage which moves in at least one direction,wherein said optical system comprises: a first optical system comprisingtwo cylindrical array lenses for partitioning the laser beam in a firstdirection which is perpendicular to a second direction in which thelaser beam is moving; a second optical system for joining thepartitioned laser beams by said first optical system on the irradiationsurface; a third optical system for partitioning the laser beam in athird direction which is perpendicular to said first direction andperpendicular to said second direction; and a fourth optical system forjoining the partitioned laser beams by said third optical system on theirradiation surface.